The present invention is directed to transparent and variable refractive index coatings, particularly to the fabrication of such coatings from a copolymer of two or more of the following monomers: tetrafluoroethylene, 2,2-bistrifluoromethyl-4,5 difluoro-1,3 dioxole, perfluoroallyl vinyl ether, and perfluorobutenyl vinyl ether, hereafter referred to as a "perfluorinated amorphous polymer", and more particularly to variable index optical single layers and multilayers, and laser-damage-resistant coatings formed by physical-vapor-deposited perfluorinated amorphous polymers (PAP).
Various types of optical coatings have been developed for different applications, and numerous processes have been developed over the years. These prior efforts are exemplified by U.S. Pat. Nos. 4,545,646 issued Oct. 8, 1985 to M. Chern et al.; and U.S. Pat. No. 4,925,259 issued May 15, 1990 to J. L. Emmett.
Polymer materials have been widely used for coatings. Perfluorinated amorphous polymer coatings have been used as thermal barriers, microelectronics insulators, and in doped optical fibers. However, there has been a need for alternate optical coating materials for use in the ultra-violet (UV), visible, and near-infrared (NIR) regime due to a shortage of dielectrics with a low refractive index. Also, with the continuing development of high energy laser systems, there is a need for high laser-damage-resistant optical coatings operating at optical wavelengths of less than 2000 nm.
This prior need has been satisfied by the present invention by the recognition that single layers of polymer materials, such as perfluorinated amorphous polymers (PAP), can be physical-vapor-deposited from bulk perfluorinated amorphous polymers, which are highly transparent in the UV-visible-NIR regime and also has a low refractive index. Also, by this invention, optical multilayers can be made by physical-vapor-deposited PAP with other physically-vapor-deposited dielectric materials. Also, by this invention the refractive index of the optical layers may be varied by simply varying the deposition rate. Thus, transparent optical coatings having a refractive index in the about 1.10-1.30 range have been produced by this invention. Thus, multilayered optical reflectors have been made by this invention.